Every time I go into a store I keep an eye out for cheap stuff that's hackable. I've been seeing in CVS pharmacy and a few other places the "Thunder Tumbler" or similarly named R/C car. CVS has had in the past good hackable toys so I thought to take a chance and see what you got for $9.99 plus tax. Turns out, you get a sweet little robot platform that has some things going for it.
* Dual motors and skid steering. Motors, gearboxes and wheels are already assembled and mounted on a chassis. Not the best of chassis but still it's workable. The motors where designed to run at 6V at full speed, but we don't need nearly the top speed this toy was meant to do so four rechargeable AA batteries (4.8V) should work fine.
* The printed circuit board that drives the toy itself is a basic single sided board with though-hole components, not surface mount. This is the key thing that makes this toy a sweet hackable deal. It has a transistor based H-bridge with forward and reverse for each motor. You can hack into the PCB with a little desoldering and presto, that dual channel h-bridge is now doing your bidding.
* The data signals for the h-bridge can be plain old 5v, straight out of your microcontroller. It will probably work with 3.3V signals as well, I just haven't tried it.
* As mentioned the chassis is OK but not great. Still, it allows me to mount my normal setup for this sort of thing, a solderless breadboard with an arduino clone attached. (The DC boarduino from adafruit industries).
* The built-in battery case takes (4) AA's. Four rechargeable ones works out great as the motor power supply.
* They even give you a 9V battery which I use to power the microcontroller via the boarduino's voltage regulator. Having separate batteries for the motors (the rechargable AA's) and for the data/control electronics (microcontrollers, sensors, etc) is a good idea to cut down on interference problems.
Step 1: Tools and Materials
To start you'll need a Thunder Tumbler R/C Car, available from many stores.
Along with that, you need a power source for the motors. I would suggest four AA batteries (rechargeable or not) that go into the regular battery slot on the car.
The point of this whole thing is to turn this toy into something that can be controlled easily with a microcontroller, so you should have your own microcontroller and know how to program it. The basic hack is controller neutral but does have some requirements:
* To control both left and right motors in forward and reverse, you need 4 digital outputs from the controller, preferably PWM outputs for all 4 so you can control the speed of the motors. That's for the simple, basic hack. The arduino has 6 PWM outputs, so I was covered there. A more advanced hack can get that down to 2 PWM outputs and 2 regular digital outputs needed for controllers with less PWM ability. However after playing around with it I found the effort needed to do so was not worth it. YMMV. I will describe the more advanced hack and what it will take to accomplish.
* I tested it with a 5V controller, so 5V data signals to the h-bridges. This worked well. They probably would work with 3.3V signals, but that has not been tested.
* I desoldered the standard DIP package 16 pin chip on the PCB and replaced it with a 16 pin IC socket. You can do that or put in headers of some flavor if you so wish. Really it's about what will work for you, just have something that allows you to connect into your controller as needed.
Tool wise, you'll need things like a #1 phillips screwdriver, an xacto knife or other cutting tool, a soldering iron and desoldering ability of some sort. I never could get the sucking up desoldering tools to work well so use the copper mesh stuff instead. Again, YMMV.